1. Field of the Invention
The present invention generally relates to a method for performing uniform processing in multiple reaction chambers sharing a gas supply system.
2. Description of the Related Art
In order to increase throughput of processed wafers, multiple wafers are loaded in a reaction chamber and processed simultaneously, by executing batch programs. However, it is difficult to perform processing with high precision using batch programs. On the other hand, if a single wafer is loaded in a reaction chamber and processed, the process can be controlled with high precision, but throughput suffers. If multiple reaction chambers of the single-wafer processing type are combined and share a process gas supply system, by operating the multiple reaction chambers simultaneously, throughput can be increased. However, when the Multiple reaction chambers share a common process gas supply system provided with a common bottle (reservoir) containing a liquid precursor, and a vaporized precursor is supplied to the multiple reaction chambers simultaneously, because of differences in pipe length from the bottle to each reaction chamber, differences in conductance of the supply line for each reaction chamber, etc it is difficult to supply a vaporized precursor equally to all the multiple reaction chambers, creating variations among the reaction chambers in terms of deposition rate, film uniformity, film composition, etc. The above variation problem in the multiple reaction chambers of the single-wafer processing type can greatly be alleviated, by conducting the process in the multiple reaction chambers in sequence, i.e., starting the process in the multiple reaction chambers in sequence with a certain delay (supplying a vaporized precursor to the multiple reaction chambers in sequence at shifted timing) wherein the process is repeated in the sequence to process multiple wafers in the multiple reaction chambers. The above sequential process works well to reduce variations in film quality among the multiple reaction chambers if the precursor has a relatively low vapor pressure, i.e., the quantity of the precursor is relatively low and thus, the precursor can readily be purged from the gas supply system.
However, if the precursor has a high vapor pressure (e.g., trimethyl phosphate, TMPI, has a vapor pressure of 2.27 kPa at 25° C., whereas bisdiethyiaminosilance, BDEAS, has a vapor pressure of 0.436 kPa at 25° C.), the quantity of the precursor is large, i.e., it is difficult to fully purge the gas from the gas supply system. The present inventors discovered that when using a precursor having a high vapor pressure in a parallel cyclic processing system of multiple reaction chambers sharing a gas supply system, variations of film properties among the reaction chambers occurred depending on the order in which the reaction chambers started processing.
Any discussion of problems and solutions in relation to the related art has been included in this disclosure solely for the purposes of providing a context for the present invention, and should not be taken as an admission that any or all of the discussion was known at the time the invention was made.